Field of the Invention
The present invention relates to a fixing device that fixes a toner image to a recording medium, and an image forming apparatus using the fixing device, such as a copying machine, a printer, a facsimile machine, or a multifunction machine having the functions of a copying machine, a printer, and a facsimile machine. More particularly, the present invention relates to a fixing device in which a heating rotator and a pressure rotator that can be pressed against each other and be separated from each other are rotated while being pressed against each other, and a toner image formed on a recording medium is thermally fixed at a nip portion between the heating rotator and the pressure rotator. In this fixing device, a separating member for separating the recording medium having the toner image thermally fixed thereto from the nip portion can be brought close to and be moved away from the nip portion between the heating rotator and the pressure rotator. In cases where the heating rotator and the pressure rotator pressed against each other are separated from each other, and where the heating rotator and the pressure rotator in a separated state are pressed against each other, the separating member is prevented from coming into contact with the heating rotator and the pressure rotator, and from scratching these rotators.
Description of the Related Art
In a conventional image forming apparatus, such as a copying machine, a printer, a facsimile machine, or a multifunction machine having the functions of these machines, a recording medium having a toner image transferred thereonto from a photosensitive member or the like is normally guided to a fixing device, and the toner image is fixed to the recording medium by the fixing device.
In such a fixing device, a heating rotator and a pressure rotator that can be pressed against each other and be separated from each other are rotated while being pressed against each other, and a toner image formed on a recording medium is thermally fixed at the nip portion between the heating rotator and the pressure rotator.
Also, in such a fixing device, a recording medium having a toner image fixed thereto might not be appropriately separated from the nip portion between the heating rotator and the pressure rotator, and might be wound around the heating rotator or the pressure rotator. To prevent this, a separating member is provided in the vicinity of the nip portion between the heating rotator and the pressure rotator. With this separating member, a recording medium having a toner image fixed thereto is prevented from being wound around the heating rotator or the pressure rotator.
In such a fixing device, a metal roller that does not have any elastic material such as rubber on its outer circumferential surface and has a reduced outer circumferential thickness is used as the heating rotator. The heating rotator formed with such a metal roller is quickly heated, and a toner image can be thermally fixed to a recording medium with high efficiently in a short period of time.
In the case of such a heating rotator formed with a metal roller that does not have any elastic material such as rubber on its outer circumferential surface and has a reduced outer circumferential thickness, the outer circumferential surface is not deformed like rubber, and therefore, the characteristics of separation of a recording medium from the heating rotator becomes poorer. Therefore, when a recording medium having a toner image fixed thereto is separated from such a heating rotator with a separating member, the separating member needs to be brought into contact with the outer circumferential surface of the metal roller, or the separating member needs to be brought very close to the outer circumferential surface of the metal roller.
In a case where the separating member is brought into contact with the outer circumferential surface of the metal roller, however, the separating member leaves a streaky surface on the outer circumference of the metal roller, resulting in streaky noise in a formed image. Also, in a case where a metal roller having a reduced outer circumferential thickness is used as the heating rotator as described above, the heating rotator formed with the metal roller is greatly deformed when the pressure rotator is pressed against the heating rotator. If a separating member is brought very close to the outer circumferential surface of the heating rotator in such a state, the separating member comes into contact with the outer circumferential surface of the heating rotator when the greatly deformed heating rotator regains its original state after the pressure rotator is separated from the heating rotator to clear a jam or the like. As a result, the outer circumferential surface of the heating rotator is scratched, and noise appears in the formed image.
To counter this, JP 2002-91221 A, JP 2007-225754 A, JP 2014-215355 A, and JP 2015-28582 A each disclose a technology by which a separating member located close to the outer circumferential surface of a heating rotator is moved away from the outer circumferential surface of the heating rotator in synchronization with an operation to separate a pressure rotator from the heating rotator against which the pressure rotator has been pressed as described above.
However, in a case where the separating member is moved away from the outer circumferential surface of the heating rotator in synchronization with an operation to separate the pressure rotator from the heating rotator against which the pressure rotator has been pressed, the separating member might come into contact with the outer circumferential surface of the heating rotator and scratch the outer circumferential surface of the heating rotator when the deformed heating rotator regains its original state. Particularly, in a case where the pressure rotator is pressed against a heating rotator formed with a metal roller having a reduced outer circumferential thickness as described above, the deformation of the heating rotator is greater. If the pressure rotator is separated from the heating rotator while the separating member is located very close to the outer circumferential surface of the heating rotator as described above, the separating member comes into contact with the outer circumferential surface of the heating rotator and scratches the outer circumferential surface of the heating rotator before moving away from the outer circumferential surface of the heating rotator.